The Pond Dynamics/Aquaculture CRSP has been studying the dynamics of tilapia production ponds in the tropics subjected to differing nutrient additions since the initiation of field experiments in January 1984. A low level of phosphorus, as triple-superphosphate, was added to ponds during the rainy and dry seasons of the first year's experiments; fish yield was less than half that expected due to, in the case of Honduras, severe clay turbidity in all ponds. During the Cycle II dry season, organic and inorganic forms of nutrients were tested. Similar amounts of nitrogen and phosphorus as layer chicken litter, dairy cow manure, or chemical fertilizer (urea and triple-superphosphate) were added to ponds. Fish yields were greater when organic fertilizer was used. However, in the chemical fertilizer treatment, fish yield was greater than that obtained during the first year's experiments, probably resulting from the greater quantities of phosphorus added, the inclusion of nitrogen, or a combination of both factors. Fish yield during the Cycle II rainy season was also greater when chicken litter was the nutrient source. Hence, organic fertilization resulted in greater fish yield than did chemical fertilization, as both autotrophic and heterotrophic production were stimulated by the former; also, fish may have consumed some manure directly. In an attempt to generate information of more immediate practical applicability to the host countries, and because chicken litter had proven to be a productive nutrient source, the CRSP initiated the present study to determine the yield of tilapia in ponds fertilized with differing rates of chicken litter. Weekly applications of layer chicken litter were made at rates of, on a total solids (TS) basis: 125 kg, 250 kg, 500 kg, and 1000 kg/ha. Additionally, the effect of season on tilapia yield was studied. (Author abstract).